Monday, May 4, 2015

What is capacitor? How capacitor stores charge? How big is Farad?

Capacitor is used to store the
energy but the process how capacitor stores energy will be discussed in this
article. Capacitor is also known as condenser. It is used both in electrical
and electronic circuits and they are available in smaller sizes from Picofarad
to KVAr. Capacitors have wide applications in electrical systems such as for
starting of single phase motors. Capacitors are also used for providing
reactive power so as to improve power factor which will leads to lower
electricity bill and lower burden on Generating station.

Capacitors are also used in :-

1.Oscillation
circuits

2.They are
used to smooth rectified AC Outputs.

3.Radio
receivers for tuning.

4.Time
delay circuits

5.Electrical filters.

Units of capacitor are Farad.
It is symbolized by Letter “F”. A Farad is defined as “the capacitance
when a potential difference of one volt appears across the plates when
charged with one coulomb.”

Capacitors used in day to day
activity are Mircofarad i.e. 10-6

Capacitor Symbol:-Capacitor symbols are as shown below:-

You Know how big is the Farad is?? Let’s have an idea how big size of plates are required to get a value of just
one Farad with a reasonable plate separation of just say 1mm operating in a
vacuum. If we rearranging the equation for capacitance above this would give us
a plate area of:

C= Q/V= permittivity, ( ε )X
Area of plates

Distance between
Plates

For air as dielectric medium Value
of Permittivity is = 8.85pF/m

Put the values into formula we get:-

A = (C)d ÷ 8.85pF/m = (1 x 0.001) ÷ 8.85×10-12 = 112,994,350 m2

or 113
million m2 which would be equivalent to a plate of more
than 10 kilometres x 10 kilometres (over 6 miles) square. That Value is very
huge and is practically not possible.

How Capacitor store Charge??

Two Parallel Plates form a
capacitor. When capacitor is connected to DC supply then one side of plate is
get positive charged and other get negative charges depending upon polarity of
DC supply. I.e. how they store the charge i.e. store energy. If plates are kept
on charge in air beyond a certain limit then plates will start getting discharged
by spark getting produced due to excessive charge.To increase the amount of
stored charge a dielectric medium i.e. a non conducting medium placed between
plates. This medium also act as spark blocker .

Types of Dielectric Medium:-

§Some of dielectric material used in commercial capacitors :-

1.Paper

2.Plastic film

3.Mica

4.Glass

5.Ceramic

6.Air.

The electrical energy is stored
in the capacitor in the form of electrostatic field.